A number of studies have reported alterations in immunocompetence in malnourished children in developing countries and in hospitalized surgical and oncologic patients. However, much of the data are conflicting and no study has, as yet, definitively ascribed the immune changes in malnutrition. The proposed animal models for protein-calorie malnutrition and Vitamin A deficiency using defined diets and experimental conditions will permit the isolation and evaluation of the influence of individual nutrients on a number of immune parameters. To evaluate whether secondary changes in nutrient metabolism or retention may contribute to changes in immunocompetence, the serum and liver levels of protein, Vitamin A, B6, zinc and copper will be measured. In addition, inbred female rats chronically protein malnourished will be infused with a total parenteral nutrition solution to assess the adequacy of that solution to promote immunocompetence. Rats will be assessed in vivo for their ability to mount a pure delayed hypersensitivity response to azobenzearsonate-tyrosine and for their ability to produce circulating antibodies to allogeneic sheep red blood cells. Lymphocytes from normal and malnourished rats will be compared with regard to: (1) their ability to produce antibody; (2) their response to mitogen stimulation; and (3) their ability to respond to allogeneic cells. This approach, using both in vivo and in vitro assessment of immune competence, will provide new data concerning the etiology of the immune response and, potentially optimal treatment of patients with infections and cancer who are further compromised by malnutrition.